RG meiosis&geneticvariation

• how is DNA from one generation passed onto the next?

  by gametes
• what are gametes in males/females?

  males- sperm cells

  females- egg cells
• when do gametes join together?

  at fertilisation to form a ZYGOTE , which divides and develops into a new organism
• what do normal body cells have, in terms of chromosomes?

  normal body cells have the diploid number (2n) of chromosomes which means that each cell contains 2 of each chromosome- one from mother one from father
• what do gametes have, in terms of chromosomes?

  Haploid number (n) of chromosomes- there is only one copy of each chromosome
• what happens at fertilisation?

  a haploid sperm fuses with a haploid egg, making a cell with the normal diploid number of chromosomes

  half the chromosomes are fro m the father and half are from the mother
• what can any sperm do during sexual reproduction?

  any sperm can fertilise any egg- FERTILISATION IS RANDOM
• What does random fertilisation produce?

  zygotes with different combinations of chromosomes to both parents. This mixing of genetic material in sexual reproduction increases genetic diversity within a species
• what is meiosis a type of?

  cell division
• what forms gametes?

  meiosis
• where does meiosis happen?

  in the reproductive organs
• cells that divide by meiosis are......?

  diploid
• what are the cells formed by meiosis?

  haploid
• what happens during meiosis?

  the chromosome number halves
• What do chromatids do in meiosis 1?

  cross over.
• what happens during meiosis 1 (crossing over) ?

  homologous pairs of chromosomes come together & pair up.

  The chromatids twist around each other and bits of chromatids swap over. The chromatids still contain the SAME GENES but now have a different combination of ALLELES
• what does meiosis produce?

  genetically different cells
• what are the two main events during meiosis which lead to genetic variation?

  crossing over of chromatids

  independent segregation of chromosomes
• what does the crossing over of chromosomes in meiosis 1 mean?

  that each of the 4 daughter cells formed from meiosis contains chromatids with DIFFERENT ALLELES
• explain crossing over briefly with steps?


  MEIOSIS 1:

  • the chromosomes of homologous pairs come together
  • chromatids cross over
  • one chromosome from each homologous pair ends up in each cell
  • MEIOSIS 2:
  • Each cell has a different chromatid and therefore a different set of alleles, which increases genetic variation
• Explain independent segregation of chromosomes (step by step)?

  1. Each homologous pair of chromosomes in cells is made up of one chromosome from mum(maternal) and one from dad(paternal)
  2. when homologous pairs are separated in meiosis 1, it is random whcih chromosome in each pair ends up in which daughtercell
  3. so the 4 daughter cells produced by meiosis have completely different combinations of those maternal & paternal chromosomes
  4. this is called independent segregation of chromosomes
  5. this 'shuffling' of chromosomes leads to genetic variation in any potential offspring
• Give the outcomes of MITOSIS?


  • produces cells with the same no of chromosomes as parent cell
  • daughter cells are genetically identical to each other and to the parent cell
  • produces 2 daughter cells
• give the outcomes of MEIOSIS?

  • produces cells with 1/2 the no of chromosomes as the parent cell
  • daughter cells are genetically different from one another and the parent cell
  • produces 4 daughter celsl
• how many daughter cells produced from mitosis?

  2
• how many daughter cells produced from meiosis?

  4
• how many divisions does mitosis have?

  1- which separates the sister chromatids
• how many divisions does meiosis have?

  2 - which separate the homologous pairs and then the sister chromatids
• give one reason why the outcomes of meiosis and mitosis are different?

  there is no pairing or separating of homologous chromosomes in mitosis, and so no crossing over or independet segregation of chromosomes. this produces genetically identical daughter cells- UNLIKE MEIOSIS